The effect of different ratios of nano-sized hydroxyapatite fillers on the micro-tensile bond strength of an adhesive resin.

The purpose of this study was to evaluate the micro-tensile bond strength (μTBS) of dentin bonding agents containing different ratios of nano-sized hydroxyapatite fillers (HA). X-ray diffraction analysis was used for characterization, and scanning electron microscope (SEM) analysis was used to determine the HA particle size after that HA were mixed a bonding agents without filler. Dentin bonding agents were divided into four groups according to addition of different ratios of nano-sized hydroxyapatite fillers as 2% HA, 5% HA, 7% HA, and no-filler control group. The teeth (n = 32) were sectioned with a low-speed diamond blade under water cooling to expose the mid-coronal dentin. Following the bonding application, restorations were applied incrementally. Each tooth was cut on the x and y axis, and each specimen was fixed to a testing device and stressed until failure occurred. The debonded specimens were examined under 250× magnification without a coating layer at 2.00 kV using a SEM to determine failure patterns. μTBS data were analyzed using a anova and Tukey's post hoc test. The failure mode data were analyzed using the Chi-Square test. The maximum mean value of μTBS was in the 7% HA group, while the minimum mean value of μTBS was observed in the control group. 7% HA group was statistically significant and higher than other groups while there were no significant differences between the control, 2% HA, and 5% HA groups. According to SEM analysis, fracture analysis revealed that the mixed fracture type was seen more often than the other fracture types. The particle size and amount of HA fillers added to the adhesive resin seem to affect the success of the bond strength to the dentin. Adding different ratio nano-sized HA fillers to the adhesive resin contributed positively to the immediate μTBS values in the dentin.